This invention relates to apparatus for examining the human cranium by means of radiation such as X or .gamma. radiation, and more particularly to a data transfer cap for the cranium which superimposes in the x-ray print a grid which assists the physician in determining the location of a brain lesion, etc.
Computerized tomography scanning devices have been developed for use in producing tomographic x-ray images, particularly images of the skull, as a laminagraphic object. The human head is inserted in a recess of the equipment and radiation is directed through the head from an external source, usually in the form of a set of pencil beams or rays toward detector means disposed on the opposite side of the head. Each ray is detected after it has passed through the body and absorption of radiation by contents of the body disposed along the path in the body followed by each ray is determined. Both the source and the detector means are orbited about the head so that radiation is directed in sets of rays through a plane of the head from a plurality of different directions. In this way the absorption or transmission coefficients of the elements in a two-dimensional matrix of elements can be determined and the result is a plurality of radio graphs that illustrate a plurality of x-ray "slices" or planes through the head.
While the prior art equipment has been very successful in detecting the presence and sizes of lesions and other features of the brain and skull, the precise location of the lesions, etc. is more difficult to determine. It is very difficult to insert a patient's head in the equipment at the precise angle desired, and therefore the data obtained is substantially unreliable. The infinite variety of possible angulations of the computerized tomography image slices about the "ideal" angle of 25.degree. to the infraorbito-meatal line of the human head causes the readout to be unreliable. Due to patient disability or incooperation and simple inadvertent malpositioning, the ideal angle of 25.degree. is often not obtained. This has the effect of placing the sagittal site of a demonstrated lesion in an arc of angles, any of which are theoretical possibilities for the position of the detected lesion, depending on the exact patient position at the time the scan was performed. Even though the scan indication may be of excellent quality, the angulation from the infraorbito-meatal as judged from the CT image is only a very rough estimate of the actual location of the lesion. The lesion can lie at any specific scan angulation within realistic limits, at any point along a vertical arc.
Because of this problem in transfer of location of detected CT abnormalities to the patient, smaller lesions and lesions located over the cerebral convexities can prove to be exceedingly difficult to find in the operating suite, which is likely to cause unnecessary surgical trauma and prolonging of the operative period.